The present invention relates to a method of deoxidation casting and a deoxidation casting machine, more precisely relates to a method of deoxidation casting, in which a molten metal left in a feeder head is properly treated, and a deoxidation casting machine capable of executing said method.
There are many kinds of ways of casting aluminum or aluminum alloy. For example, gravity casting can be executed in a simple casting die and is capable of improving quality of products. A conventional method of aluminum gravity casting will be explained with reference to FIG. 14. A splittable casting die 100 is made of a metal and constituted by a lower die section 102a and an upper die section 102b. A cavity 104, in which a product will be cast, is formed between the die sections 102a and 102b. 
A molten metal inlet 106, from which a molten metal, e.g., molten aluminum, is poured, the cavity 104 and a feeder head 108, which is provided between the inlet 106 and the cavity 104, are formed in the upper die section 102b. Further, air ventilation holes 110, which discharge air in the cavity 104 when the molten metal is introduced into the cavity 104, are also formed in the upper die section 102b. 
When the molten metal is solidified, about 3% of volume of the molten metal is contract. By the contraction of the molten metal filled in the cavity, a contracted part is formed in the cast product. In the casting die 100 shown in FIG. 14, the molten metal in the feeder head 108 moves toward the contracted part, by its own weight, when the molten metal in the cavity 104 is solidified. Then, the molten metal fed from the feeder head 108 fills the contracted part, so that no contracted part is formed in the cast products. Since the molten metal is supplemented from the feeder head 108 to the cavity 104 by its own weight, volume of the feeder head 108 must be great.
Fluidity of the molten metal is low in the casting die 100, so weight of the molten metal in the feeder head 108 must be heavy. Therefore, the volume of the feeder head 108 must be great so as to compulsorily supplement the molten metal. In the case of aluminum casting, for example, aluminum is apt to oxidize, so an oxide film is formed on the surface of the molten aluminum, so that the fluidity of the molten aluminum must be lower. To improve the fluidity, lubricant is applied to inner faces of the cavity 104.
To improve the fluidity of the molten aluminum and to cast a product having good external appearance without applying the lubricant, the inventors of the present invention invented a method of aluminum casting (see Japanese Patent Gazette No. 2000-280063). The method will be explained with reference to FIG. 15. A deoxidizing compound, e.g., magnesium nitride compound (Mg3N2), is introduced into the cavity 104 of the casting die 100, then the molten aluminum or aluminum alloy is poured into the casting die 100. The deoxidizing compound deoxidizes the oxide film formed on the surface of the molten aluminum or aluminum alloy, so that surface tension of the molten aluminum or aluminum alloy can be reduced, the fluidity thereof can be improved, and the product having no casting-wrinkles can be produced. Namely, high quality products can be cast.
The method using the deoxidizing compound is capable of improving the fluidity of the molten metal and well filling the molten metal in the cavity. The volume of the feeder head 108 can be reduced because the molten metal is capable of well filling the cavity 104 without using the weight of the molten metal in the feeder head 108. Therefore, the volume of the feeder head 108 may be designed on the basis of the volume reduction of the solidified metal.
In the conventional casting machine, the metal solidified in the feeder head 108 is integrated with the product solidified in the cavity 104. The metal solidified in the feeder head 108 must be cut and removed from the cast product. The removed metal will be reused as a casting material. As described above, the step of removing a disused solidified metal from the product is an essential step in the conventional method. If the volume of the feeder head 108 is great, it takes a long time to remove the disused metal. Further, energy consumption must be increased so as to melt the disused metal, which has the great volume, to reuse.
On the other hand, in the improved method disclosed in the Japanese Patent Gazette No. 2000-280063, the volume of the feeder head 108 can be designed to supplement the contracted part of the product, so the volume of the feeder head 108 can be reduced. By reducing the volume of the feeder head 108, the volume of the disused metal is also reduced, so the disused metal can be easily cut and removed from the cast product.
However, if the volume of the feeder head 108 is too small, the contracted part is formed in the vicinity of a connecting part between the disused metal and the cast product. In some cases, the contracted part is formed in the cast product. Further, if the molten metal left in the small feeder head 108 can be removed or discharged therefrom, working efficiency of the casting can be improved.